Process of producing trichromatic half-tone-process negatives.



Nu. 707,42l. Patented Aug: l9, I902.

F. E. was. PROCESS OF PRODUCING TRICHRDMATIC HALF TUNE PROCESS NEGATIVES.

(Application filed June 30, 1902) (No Model.)

THE ucnms PETERS co mo'rauruo. WASHINGTON. n. r.

40 No. 668,989, dated February 26, 1901.

UNITED STATES PATENT @rrlcn.

FREDERIO E. IVES, OF PHILADELPHIA, PENNSYLVANIA.

PROCESS OF PRODUCING TRICHROMATIC HALF-TONE-PROCESS NEGATIVES.

SPECIFICATION forming part of Letters Patent No. 707,421, dated August 19, 1902.

Application filed June 30,1902. Serial No. 113,732. (No specimens.)

T aZZ whom it may concern.-

Beit known that I, FREDERIO E. IvEs, a citizen of the United States, residing in Philadelphia, Pennsylvania, have invented an Improved Process of Producing Trichromatic Half-Tone-Process Negatives, of which the following is a specification.

The object of my invention is to simplify, expedite,and cheapen the production of printing-surfaces for the trichromatic printing process.

In my Patent No. 432,530, dated July 22, 1890, is set forth a principle by the application of which a correct record of all the colors I5 of objects is obtained in three photographic images which are adapted to be used in the production of heliochromic pictures by means of pigments. The importance of such color analysis as therein set forth having been experimentally demonstrated, it was found that the preservation of the exact ratios of exposure and opacities in the three negative images (a very important element in the perfeotion of the complete record) could not be insured when the three negatives were exidentical in perspective and preferably upon a single sensitive plate, although three separate plates could be used with success if exposed and developed together. This procedure has been made practicable by my invention of special cameras described in the following United States patents: No. 432,530, dated May 17, 1892; No. 546,889, dated September 24:, 1895; No. 655,712, dated August 14, 1900; No. 660,442, dated October 23, 1900;

Trichromatic photography as applied to the projecting-lantern and photochromoscope was never carried out successfully as a commercial process until such means were provided for automatically keeping the exposure and density ratios in the sets of negative and positive images. The same relations have been preserved in photographic-printing processes in which the three positive prints are made at one time in one sheet of bichromated gelatin and the colors introduced after developing and cutting apart the separate images.

In each case what were originally three separate and distinct operations, involving three chances and probabilities of error in exposure ratios and three more in density ratios, are now reduced to practically one operation, with no chance of error when the devices are once perfectly adjusted. In the application of the process to the production of colorprints by the so-called half-tone process the automatic character of the procedure has been lost, making much skilful correction necessary in most cases and greatly detracting from the character and success of the work, owing to the necessity for disposing the lined screens at different angles with reference to the separate images to avoid a wa tered-silk pattern effect in the color-prints. This necessity has been met by making the half-tone negatives separately and changing or turning the screen between the operations, and this involves not only extra time and labor, but multiplied chances of error. I propose to make the automatic character of the procedure extend throughout these operations by employing three half-tone screens or their equivalent with different disposition of their patterns in the simultaneous production of the three half-tone negatives, so that the required pattern is given to all three images at one operation, preserving the ratios of gradation and permitting the printing upon metal or stone and subsequent operations for completing the printing-surface to be carried on as one operation instead of three.

In the accompanying drawings, Figure 1 is a representation of the varying angles of the lines on the screens employed, only two lines of each screen being shown. Fig. 2 is a diagrammatic view of a camera having three lenses which may be employed in carrying out my invention. Figs. 3 and 4 are views illustrating modifications of the invention when employed in connection with a camera having three lenses, and Fig. 5 is a View illustrating a method of carrying out the process by the use of a camera having a single lens.

Assuming that the ordinary cross line screen of the commercial half-tone process is to be employed, I prefer to employ one with three sections or a set of three, the lines in the different screens or screen-sections being disposed at about the angles as indicated in Fig. 1, in which 1 represents the angle for the red record, 2 the angle for the blue record, and 3 the angle for the green record, the printing-inks used with the respective plates being green-blue, yellow, and crimson. The benefit of this procedure is most directly utilized by placing such a set of screens directly in front of the sensitive plate in a camera intendedto produce simultaneously the three color-records, in which case, with suitable adjustments, a set of half-tone negatives can be made at one operation direct from the object, and subsequently from these negatives the three printing-surfaces also by one procedure instead of three. It is not, however, possible to do this with any of the patented cameras referred to when they are constructed and adjusted in the manner in which they have been and naturally would be for the purpose for which they were originally intended, which is merely to produce triple color-records which are not broken up into lines and dots, as required, for the direct production of half-tone-process plates. Heretofore in the production of such triple cameras to be used for producing trichromatic negative-records advantage has been taken of the fact that the divided incident ray can be passed through separate diaphragm-apertures to so vary the relative size of these apertures as to compensate for the unequal sensitiveness of the photographic plate to the different groups of colored light-rays forming the three images. It is sufficient for all of the ordinary purposes of such a camera that the diaphragms be concentrically superposed optically when viewed from the front of the camera, under which conditions the diameter of the apertures may be varied for the purpose of compensating for unequal sensitiveness for different colors, as before stated. When, however, such a camera is employed in connection with the three ordinary cross-lined sealed process-screens, as required for carrying out myinvention in the most direct manner, it is necessary that the size of the apertures bear a definite relation to the character and position of the process-screens and that other means than alteration of diaphragm-apertures be resorted to to equalize the light action in a simultaneous exposure for the three images. This will be made clear by a consideration of the dioptrics of graduated line-and-dot formation, which is the basis of successful halftone-screen process negative-making. In order that the lines or dots may be graduated in size to properly represent the gradations of light and shade, the screen is removed to a sufficient distance-say, a quarter of an inchfrom the surface of the sensitive plate, so that the opaque lines of the screen cast shadows upon the sensitive plate, which shadows are not sharply defined, but have a graduated penumbra, the width of which is controlled by the relation of the size of the pencils of rays admitted by the lens-aperture to the width of the opaque lines of the screen and the distance of those lines from the surface of the sensitive plate. Proper control of these relations results in the production of the shaded line, which is technically known as the optical V and bears the same relation to the half-tone process that the V-shape tool of the engraver does to wood engraving. Therefore when such triple cameras as Ihave described are to be adapted to the simultaneous production of three half-tone-process negatives through three different'color-screens thediaphragm-apertures must be made equal or at least adjusted to meet the screen process requirements, and the equalization of light action for the three images can then be secured by another device. For this purpose it is permissible to insert at any suitable point in the path of either divided ray a plane glass having an even coating of transparent, preferably smoke-colored, ,varnish. The depth of tint of the compensating screens can be regulated by coating the glasses with the colored varnish in various degrees of dilution and the correct compensation can be found by a process of trial and error. It would be possible to secure approximate compensation by suitableintroduction of black in the colorscreens themselves; but such means are neither commendable nor permanently efficient, because the compensation generally has to be altered somewhat for every dilferent batch of sensitive plates, and by means of the colored varnishes this can be done with far greater facility and accuracy without disturbing the selective color-screens.

When fiat surfaces, such as paintings and colored drawings on plane surfaces are to be reproduced, a camera such as shown in Fig. 2 maybe employed. In this figure, 1, 1 and 1 represent rectilinear lenses having diaphragms m of uniform aperture and preferably arranged to permit of adjusting the distances of 1 and 1 in respect to 1 by means of sliding plates 7, and 4 and 5 are partitions, also preferably adjustable from and toward each other.

1, 2, and 3 are the screen-sections of Fig. 1, 6 the sensitive plate or plates, and 14, 15, and 16 the selective color-screens, these screens being preferably mounted on the camerafront back of the lens-tubes, as shown, although they may be otherwise disposed without departing from the essential feature of my invention.

17 and 18 are screens for compensating for the different effects of light in connection with two of the color-records, and such screens may be employed for each of the records, if desired, or other compensating devices may be employed. For instance, in Fig. 3 I have shown rotating sectors 20 and 21, mounted upona shaft or axle 22, to which rotating motion can be imparted by clockwork or other mechanism during the time that the exposure is being made. The sector 20 is composed of sections adjustable in respect to each other,

will pass in front of the lens-tube 1 only.

Hence by properly adjusting said sector 2L in respect to the sector 20 the passage of light through the lens 1 may be obstructed for a longer time than the passage of light through the lens 1*, the passage of light through the lens 1 being continuous. In Fig. 4 I have shown an arrangement of single sector 23,

whereby the same result is attained, the sec tor being so shaped as to obstruct the lens 1 for a longer time than it obstructs the lens 1". The separation of the points of View in this camera would render it incapable of producing three images identical in perspective except when photographing flat surfaces; but the latter form a large part of the material furnished for reproduction, and such a camera is therefore convenient and useful.

If it is desired to make the half-tone-process negatives from ordinary positive prints from a trichromatic negative-record, a singlecopying camera, with the three-section screen or three screens juxtaposed, as shown in Fig. 5, is sufficient. In this view, 9, 10, and 11 represent the images of the positive trichromaticrecord. 12isarectilinear lens. 1,2, and 3 are the screens of Fig. l, and 6 is the sensitive plate or plates.

Having thus described my invention, I

claim and desire to secure by Letters Patent- 1. The mode herein described of producing triehromatic half-toi'ie-process negatives, said mode consisting in simultaneously exposing three elements of the color-record through three half-tone-process screens having different dispositions of pattern and with dioptric light adjustment to meet the requirements of screen half-tone-process negative-making, substantially as specified. 2. The mode herein described of producing trichrom atic half-tone-process negatives, said mode consisting in simultaneously exposing the three images of a color-record through three half-tone-process screens having difierent dispositions of pattern and with dioptric light adjustment to meet the requirements of screen half-tone-process negative-making, and independent of adjustment for equalizing the chromatic light action upon the three images, substantially as specified.

3. The mode herein described of producing trichromatic half-tone-process negatives,said mode consisting in simultaneously exposing the three elements of a color-record through a single lens and diaphragm, and through three half-tone-process screens having different dispositions of pattern, substantially as specified.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

FREDERIC E. IVES. Witnesses:

F. E. BEoH'roLn, FLORENCE HILLMAN. 

